Reuse of block tree pattern in video compression

ABSTRACT

A method includes transcoding a first block from a spatial region. The first block is associated with a first block tree pattern defining a structure of splitting a block into smaller blocks. A bit string of bits for the first block tree pattern is included in an encoded bitstream. The method determines a location of the first block in the spatial region when the first block tree pattern of the first block can be reused for a second block tree pattern of a second block. The spatial region includes blocks and the location is based on the first block being in the spatial region. Information for the second block is included in the encoded bitstream that indicates the location of the first block in the spatial region. The location allows the bit string for the first block tree pattern to be retrieved for use to decode the second block.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application and, pursuant to 35U.S.C. § 120, is entitled to and claims the benefit of earlier filedapplication U.S. application Ser. No. 16/370,117, filed Mar. 29, 2019,entitled “REUSE OF BLOCK TREE PATTERN IN VIDEO COMPRESSION”, which isentitled to and claims the benefit of the filing date of U.S.Provisional App. No. 62/650,842 filed Mar. 30, 2018, the content ofwhich is incorporated herein by reference in its entirety for allpurposes.

BACKGROUND

A video transcoder transcodes and decodes video based on block treepatterns of blocks. FIG. 1 depicts an example of a frame 100 of thevideo that is divided into root blocks 102. As shown, frame 100 includesforty root blocks 102-1 to 102-N; however, a different number of rootblocks may be used. The video transcoder splits each root block 102 intoleaf blocks 104. A block tree pattern may describe how the root block issplit. That is, the block tree pattern may include more branches thatsplit a root block into more blocks. Some blocks are split into smallerblocks based on the content of the video. For example, the larger leafblocks cover flat regions in the video that do not include complexinformation (e.g., an area that includes a single color) and the smallerleaf blocks cover more complex regions in the video (e.g., an area thatincludes a person's face). The smaller leaf blocks are used to conveythe more complex information while flat regions include mostly the sameinformation and can be compressed using a larger block size.

The transcoder generates a bit string of bits to represent the blocktree pattern of how the root block is split into leaf blocks. A largeand complex block tree pattern requires a large number of bits torepresent the block tree pattern, which need to be transmitted from atranscoder to the decoder. FIG. 2 depicts an example of a bit string ofbits 204 that needs to be transmitted for a block tree pattern. Thetranscoder decides on the block tree pattern at 201. A tree structurethat represents the block tree pattern is shown at 202. This treestructure represents how larger blocks are split into smaller blocksfrom the root block. Each split divides a respective block into foursmaller blocks. The transcoder then generates a bit string of bits 204to represent the block tree pattern, and sends the bits in the bitstreamfor decoding by the decoder. The number of bits depend on the level ofsplitting that occurs. That is, if the root block is split into a largenumber of smaller blocks, then more bits are needed to represent theblock tree pattern. The more bits that are included in the bitstream,the greater the overhead of the transcoding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example of a frame.

FIG. 2 depicts an example of a bit string of bits that needs to betransmitted for a block tree pattern.

FIG. 3 depicts a simplified system for transcoding and decoding using ablock tree pattern according to some embodiments.

FIG. 4 depicts an example of reusing the block tree pattern according tosome embodiments.

FIG. 5A depicts a simplified flowchart of a method transcoding a rootblock when reusing block tree patterns according to some embodiments.

FIG. 5B depicts a simplified flowchart of a method for decoding a blockwhen reusing block tree patterns according to some embodiments.

FIG. 5C depicts an example of software code to reuse block tree patternsaccording to some embodiments.

FIG. 6 depicts an example of reusing block tree patterns that arealtered according to some embodiments.

FIG. 7A depicts a simplified flowchart of a method for transcoding aroot block when reusing altered block tree patterns according to someembodiments.

FIG. 7B depicts a simplified flowchart of a method for decoding a blockwhen reusing altered block tree patterns according to some embodiments.

FIG. 7C depicts an example of software code to reuse altered block treepatterns according to some embodiments.

FIG. 8 depicts an example of applying a patch to blocks according tosome embodiments.

FIG. 9A depicts a simplified flowchart of a method for transcoding aroot block when reusing altered block tree patterns according to someembodiments.

FIG. 9B depicts a simplified flowchart of a method for decoding a blockwhen applying a patch to a previous block tree pattern according to someembodiments.

FIG. 9C depicts an example of software code to process patches accordingto some embodiments.

FIG. 10 depicts examples of a split patch and a merge patch according tosome embodiments.

FIG. 11 depicts an example of a transcoding system according to someembodiments.

FIG. 12 depicts an example of a decoding system according to someembodiments.

DETAILED DESCRIPTION

Described herein are techniques for a video compression system. In thefollowing description, for purposes of explanation, numerous examplesand specific details are set forth in order to provide a thoroughunderstanding of some embodiments. Some embodiments as defined by theclaims may include some or all of the features in these examples aloneor in combination with other features described below, and may furtherinclude modifications and equivalents of the features and conceptsdescribed herein.

Some embodiments reduce the number of bits to signal a block treepattern that is used to split a root block into leaf blocks. Atranscoder may determine how to split a root block into leaf blocks. Thetranscoder can determine a bit string of bits that represent the split.However, instead of including the entire bit string of bits in theencoded bitstream, the transcoder searches previously used block treepatterns to determine whether there is a block tree pattern that can bereused for the current block tree pattern being currently encoded. Ifthere is a similar block tree pattern, then the transcoder may reuse thesimilar block tree pattern. For example, the transcoder can signal tothe decoder that the similar block tree pattern is being used for theroot block. The transcoder had previously signaled the bits for thepreviously used block tree pattern. Then, the transcoder does not needto include all the bits describing the current block tree pattern in theencoded bitstream. For example, the transcoder may not need to includeany bits from the bit string of bits. Rather, the transcoder may inserta flag into the encoded bitstream that indicates the block tree patternis being reused. The transcoder may also include an identifier for theroot block in which the similar block tree pattern was used.

The decoder may use the flag to determine that the root block is splitsimilarly to the block tree pattern of the previously decoded root blockusing the previously sent block tree pattern. The decoder retrieves thebit string for the block tree pattern of the previous decoded root blockand uses that bit string to decode the current root block. The reuse ofthe similar block tree pattern reduces the number bits in the encodedbitstream, which improves the compression of the video.

System Overview

FIG. 3 depicts a simplified system 300 for transcoding and decodingusing a block tree pattern according to some embodiments. System 300transcodes a source video asset, which may be any type of video, such asfor a television show, movie, or video clip. The source video may needto be transcoded into one or more formats, such as one or more bitrates.In some embodiments, a server system 302 sends an encoded bitstream toclient 304. For example, server system 302 may be sending a video to aclient 304 for playback.

Server system 302 includes a transcoder 306 that transcodes video intoan encoded bitstream. Transcoder 306 may be a software videoprocessor/transcoder configured on a central processing unit (CPU), ahardware accelerated video processor/transcoder with a graphicalprocessing unit (GPU), a field programmable gate array (FPGA), and/or ahardware processor/transcoder implemented in an application-specificintegrated circuit (ASIC). Transcoding may be the conversion from onedigital format to another digital format. Transcoding may involvedecoding the source format and encoding the source video into anotherdigital format, or converting the source content into videos with aspecific resolution, framerate, bitrate, codec, etc. Also, encoding maybe the conversion of analog source content and to a digital format. Asused, the term transcoding may include encoding.

During the transcoding, a transcoder block tree engine 308 splits eachroot block into leaf blocks as described above. Transcoder block treeengine 308 generates a bit string of bits that represent the block treepattern. For example, at 204 in FIG. 2 , a block tree pattern splitstring of bits is used to describe the block tree pattern at 201. Thebits may be flags or other information (e.g., characters) that describethe block tree pattern, such as a value of “1” indicates a split of thecurrent block and a value of “0” indicates a leaf block is reached. Aleaf block is when the block is not split any further. In this example,quad-tree splitting is performed, which splits a block into four smallerblocks. However, a block may be split into other numbers of blocks usinga triple-tree splitting structure (e.g., a block is split into threesmaller blocks), or a binary-tree splitting structure (e.g., a block issplit into two smaller blocks). Also, the shape of the blocks may alsodiffer, such as a block is split into rectangular or square blocks.Transcoder 306 may communicate the different types of splittingstructures and blocks to decoder 312. The more complicated the pattern,the more bits that are needed to communicate the structure of the blocktree pattern.

In the quad-tree split pattern in FIG. 2 the root block is split and avalue of “1” indicates a split of a block into four blocks and a valueof “0” indicates a leaf block has been reached. In the bit string at204, the first bit of “1” splits the root block into four blocks. Thenext four bits of “0111” indicate the splitting of the first level ofthe quad-tree. The value of “0” indicates block 0 is a leaf block. Thenext four bits of “0001” indicate blocks 1, 2, and 3 are leaf blocks,and then there is a split. Then the next four bits of “0000” indicateblocks 4, 5, 6, and 7 are leaf blocks. The next four bits of “0001”indicate blocks 8, 9, and 10 are leaf blocks and then there is a split.Then the next four bits of “0000” indicate blocks 11, 12, 13, and 14 areleaf blocks. Then the next four bits of “1000” indicate that there is asplit and then blocks 19, 20, and 21 are leaf blocks. The next four bitsof “0000” indicate blocks 15, 16, 17, and 18 are leaf blocks. Althoughthis method of signaling the block tree pattern is described, othermethods may be used. These flags are generated according to the blockpatterns by transcoder 306 and transmitted to decoder 312 via theencoded bitstream. Decoder 312 receives and translates these flags intothe block tree patterns, which are exactly identical to the transcoder'sblock tree patterns.

Transcoder block tree engine 308 may generate the bit string for theblock tree pattern the first time a pattern is encountered. Transcoder306 then signals the bit string to decoder 312 in the encoded bitstream.There may be times when the block tree pattern can be reused. Forexample, transcoder block tree engine 308 may determine that the currentblock tree pattern for a current root block matches a previouslyencountered block tree pattern from another root block. Also, it ispossible that the block tree patterns may not exactly match, but maystill be reused. Transcoder block tree engine 308 may also reuse theblock tree pattern when the block tree patterns do not exactly match,which will be described in more detail below. Block tree patterns may besimilar when a first block tree pattern can be reused for a second blocktree pattern. When reusing a block tree pattern, transcoder block treeengine 308 inserts a flag in the encoded bitstream to signal when toreuse a block tree pattern. The flag may indicate a location of the rootblock that includes the same block tree pattern or other information maybe included in the encoded bitstream to indicate the location of theroot block that includes the same block tree pattern.

Transcoder 306 sends the encoded bitstream for the video to decoder 312.The encoded bitstream includes the bits for the block tree patterns andalso flags that indicate block tree patterns that are reused. Client 304receives the encoded bitstream and decoder 312 then decodes the encodedbitstream. To decode the bitstream, decoder 312 needs to know howtranscoder 306 split each root block. During the decoding, a decoderblock tree engine 310 determines the block tree patterns that were usedto encode the root blocks. Also, decoder block tree engine 310determines when to reuse a block tree pattern based on signaling fromtranscoder 306. For example, decoder block tree engine 310 determineswhen a flag for reusing a block tree pattern is encountered. Then,decoder block tree engine 310 determines the block tree pattern, such asby determining the location of the root block that is associated withthe block tree pattern to be reused and then retrieving the bit stringfor the associated block tree pattern for that root block. Decoder 312uses the bit string to decode the current root block, such as bysplitting the root block according to the bit string for the reusedblock tree pattern.

Block Tree Pattern Reuse

FIG. 4 depicts an example of reusing the block tree pattern according tosome embodiments. A frame 400 is a picture of video that includes rootblocks 402-1 to 402-N. Frame 400 may include forty root blocks 402, butthe frame may be divided into different numbers of root blocks.Transcoder 306 may transcode a root block X at 402-X using a block treepattern. Transcoder 306 encodes block X without any reuse of a blocktree pattern. That is, transcoder 306 generates a bit string torepresent the block tree pattern and this bit string is included in theencoded bitstream. Transcoder 306 may store the bit string in a storagelocation to keep a record of the block tree patterns that were alreadyused.

When transcoder 306 encounters a block Y at 402-Y, transcoder 306performs the splitting of the root block into leaf blocks. Transcoder306 can then determine that block Y and block X share a similar blocktree pattern. For example, transcoder 306 may generate the bit stringthat represents the block tree pattern. Then, transcoder 306 determineswhether the bit string was previously used for another root block. Insome examples, transcoder 306 looks at the previously generated bitstrings and determines whether the same bit string was stored in thestorage. If a bit string exists, then transcoder 306 can determine thatblock Y is split into smaller leaf blocks in the same block tree patternas block X. For example, at 404, the block tree pattern for both blocksX and Y is shown. This block tree pattern includes the same types ofleaf blocks 404-1 to 404-N.

Transcoder 306 can then insert a flag, which is information thatindicates the reuse of a block tree pattern, into the encoded bitstreamthat is sent to decoder 312. In some embodiments, the flag is a bit thatcan be the value of “0” or “1”, with the value of “0” meaning do notreuse the previous tree block pattern and the value of “1” meaning reusea previous block tree pattern. Also, transcoder 306 may include thelocation of block X such that decoder 312 can determine which block treepattern to use. The location may be an identifier for the root blockthat includes the block tree pattern to reuse. In other examples, thelocation may identify a block tree pattern that has been previously sentto decoder 312. In some embodiments, the flag may be one bit to indicatethe reuse and X number of bits are used to send the location of the rootblock that includes the block tree pattern to reuse.

FIG. 5A depicts a simplified flowchart 500 of a method transcoding aroot block when reusing block tree patterns according to someembodiments. At 502, transcoder 306 transcodes root blocks from a frame.During the transcoding, transcoder 306 generates a block tree patternfor each block. At 504, transcoder 306 stores information for the blocktree pattern in storage. For example, transcoder 306 stores the bitstring for the block tree pattern.

At 506, transcoder 306 transcodes a current block from a spatial regionnear to the already transcoded blocks. The spatial region may be in asame frame as the current block being transcoded. However, the spatialregion is not limited to the same frame. For example, the spatial regionmay be in frames other than the current frame being transcoded, such asthe X frames from the current frame (e.g., the previous two frames).Also, the spatial region may belong to other layers in a multi-layervideo coding or other views in a multi-view video coding. A layer may bepart of a sequence of pictures having at least one commoncharacteristic. For example, a layer may include a particular view(e.g., perspective) of multi-view video data. In some examples, a layermay be associated with a particular layer of scalable video data. Theterms layer and view may be used interchangeably.

At 508, transcoder 306 generates a block tree pattern and correspondingbit string for the current block. Then, at 510, transcoder 306determines whether a similar block tree pattern exists. For example,transcoder 306 searches the storage for block tree patterns that can bereused for the current block. The block tree pattern may be the same ormay be slightly different. For example, as will be discussed below, ablock tree pattern that is slightly different may be rotated or alteredto match the current block tree pattern. In some embodiments, the searchprocess may compare a bit string that represents the split of the blockfor current transcoded block with other bitstrings that represent thesplit of the previously transcoded blocks. If the bit strings areexactly identical, transcoder 306 determines that the two coding blocksshare the same block tree pattern. The parsing and comparing processcould be designed to handle the scenarios of block tree patternrotation/flipping and partial block tree patch, which will be discussedbelow. For the case of block tree pattern rotation/flipping, aconversion logic can be used to translate a bit string of a block treepattern into other bit strings, which correspond to rotated versions orflipped versions of the block tree pattern. Searching withrotation/flipping can be applied by comparing the bit string of currenttranscoded block with the converted bit strings of previously transcodedblocks. For the case of partial block pattern patching, the parsing andcomparing logic can be designed to tolerate a certain level ofdifferences between the bit strings that represent the splittingstructure. The differences may include but are not limited to largestpatch block size, number of patches and etc.

At 512, if a similar block tree pattern is found, transcoder 306determines information for the reuse of the block tree pattern andinserts the information into the encoded bitstream. For example, reusingthe block tree pattern may include transcoder 306 inserting a flag inthe encoded bitstream indicating that the block tree pattern fromanother block is being used for the current block. Also, transcoder 306may add the location of the block that includes the similar block treepattern. The location of the previous block may be represented by theroot block index inside a frame or by 2-dimensional coordinates of aroot block inside a frame. Also, the location of the previous root blockmay be represented by an index of a look-up table that recordspreviously decoded block tree patterns. At 514, if a similar block treepattern is not found, transcoder 306 inserts the full description forthe block tree pattern into the encoded bitstream.

FIG. 5B depicts a simplified flowchart 530 of a method for decoding ablock when reusing block tree patterns according to some embodiments.Decoder 312 receives the encoded bitstream and can decode the bitstreaminto the video. At 532, decoder 312 selects a current block to decodefrom the encoded bitstream. At 534, decoder 312 determines if a flag isset that indicates the block tree pattern should be reused. If the flagis set to indicate that the block tree pattern should be reused, then at536, decoder 312 determines the location of the previous root block thatis associated with the block tree pattern to reuse. For example,transcoder 306 may have sent the location of the block that includes theblock tree pattern that should be reused in the encoded bitstream. At538, decoder 312 then decodes the block by reusing the block treepattern. If, on the other hand, the flag was not set at 534, at 540,decoder 312 decodes the block using the bit string in the encodedbitstream that defines the block tree pattern.

FIG. 5C depicts an example of software code to reuse block tree patternsaccording to some embodiments. At 552, decoder 312 determines the valueof the flag reuse_previous_tree_flag. In some embodiments, the value maybe a bit value of “1” to indicate the block tree pattern should bereused or a bit value of “0” to indicate no reuse; however, other valuesmay be used. At 554, if the flag is set to indicate that the block treepattern should be reused, then at 556, decoder 312 determines thelocation of the previous block tree. For example, the location is storedin the variable location_of_previous_tree. If, on the other hand, theflag was not set at 554, at 558, decoder 312 decodes the block using thestring of bits that defines the block tree pattern. Decoder 312 may usethe function tradition_decode_root_block( ) to perform the decodingprocess that does not reuse the block tree pattern.

Similar Block Tree Patterns

The block tree patterns that are determined between two root blocks maynot exactly match, but the reuse of a block tree pattern maynevertheless be possible. For example, some block tree patterns may besimilar, but are rotated or flipped from a current block tree pattern.FIG. 6 depicts an example of reusing block tree patterns that arealtered according to some embodiments. At 602 in a frame 400, four rootblocks A, B, C, and D are shown at different locations. Transcoder 306may reuse the block tree pattern for root block A when transcoding rootblocks B, C, and D. However, root blocks B, C, and D may not haveexactly the same block tree pattern. Rather, the block tree pattern forroot blocks B, C, and D are rotated from the block tree pattern for rootblock A.

At 604, the block tree pattern for root block A is shown. At 606, theblock tree pattern for root block B is different from the block treepattern for root block A. However, if transcoder 306 rotates the blocktree pattern for root block A by 90 degrees, the block tree pattern forroot block A becomes similar to the block tree pattern for root block B.Similarly, if transcoder 306 rotates the block tree pattern for rootblock A by 270 degrees, the pattern becomes similar to the block treepattern for root block C at 608. At 610, if transcoder 306 rotates theblock tree pattern for root block A by 180 degrees, the pattern becomessimilar to the block tree pattern for root block D. In some embodiments,the block tree pattern can be uniquely presented by the split bitstring, thus transcoder 306 can translate a given bit string to anotherbit string corresponding to its rotated version of block tree pattern.Transcoder 306 can analyze the similarity of block tree pattern bycomparing the current bit string with the converted bit strings.

Other alterations to the block tree patterns may also be appreciated.For example, transcoder 306 may flip the previous block tree pattern.Flipping the pattern may exchange one half of the block tree patternwith a second half of the block tree pattern. The block tree pattern maybe split horizontally or vertically. The exchange may also exchangeother portions, such as quarters of the block tree pattern may berearranged to different positions.

FIG. 7A depicts a simplified flowchart 700 of a method for transcoding aroot block when reusing altered block tree patterns according to someembodiments. The following assumes that transcoder 306 has transcodedsome root blocks and stored the block tree patterns in storage. At 702,transcoder 306 searches the storage for previous block tree patternsthat may be reused, but are not exactly the same as the current blocktree pattern. The above described use of converted bit strings may beused to determine block tree patterns that are not exactly the same asthe current block tree pattern, but may be patched. At 704, transcoder306 may then determine if the previous block tree pattern can be alteredto be the same as the current block tree pattern.

At 706, if a similar block tree pattern is found, transcoder 306determines information for the alteration of the block tree pattern.Then, at 708, in addition to inserting a flag in the encoded bitstreamindicating that the block tree pattern from another block is being usedfor the current root block and the location of the root block,transcoder 306 may insert information on how to alter the block treepattern. For example, transcoder 306 may insert information on therotation degrees or how to flip the block tree pattern. At 710, if asimilar block tree pattern is not found, transcoder 306 inserts the fulldescription for the block tree pattern into the encoded bitstream.

FIG. 7B depicts a simplified flowchart 730 of a method for decoding ablock when reusing altered block tree patterns according to someembodiments. At 732, decoder 312 selects a current root block to decodefrom the encoded bitstream. At 734, decoder 312 determines if a flag isset that indicates a block tree pattern should be reused. If the flag isset to indicate that the block tree pattern should be reused, then at736, decoder 312 determines the location of the previous block treepattern for a previous root block. At 738, decoder 312 determineswhether rotation of the previous block tree pattern is required. If so,at 740, decoder 312 rotates the block tree pattern for the previous rootblock. At 742, decoder 312 determines whether flipping of the previousblock tree pattern is required. If so, at 744, decoder 312 flips theblock tree pattern for the previous root block. It is noted that bothrotation and flipping may be performed, or only one of rotation orflipping may be performed. At 746, decoder 312 then decodes the currentroot block by reusing the altered block tree pattern. If, on the otherhand, the flag was not set at 734, at 748, decoder 312 decodes thecurrent root block using the string of bits in the encoded bitstreamthat defines the block tree pattern.

FIG. 7C depicts an example of software code to reuse altered block treepatterns according to some embodiments. At 762, decoder 312 determinesthe value of the flag reuse_previous_tree_flag. At 764, if the flag isset to indicate that the block tree pattern should be reused, then at766, decoder 312 determines the location of the previous block tree. Forexample, the location is stored in the variablelocation_of_previous_tree. Then, at 768, decoder 312 determines iftranscoder 306 set a parameter for the rotation of the previous blocktree. If so, the parameter indicates the rotation degrees, such as 90,180, and 270 degrees. Then, at 769, decoder 312 determines if transcoder306 set a parameter for the flipping of the previous block tree. If so,the parameter indicates the flipping direction, such as horizontally orvertically. Decoder 312 then decodes the block by reusing the block treepattern in conjunction with the parameters, if any, indicating therotation and flipping direction to be used. Decoder 312 may alter thebit string to represent the rotation and/or flipping.

If the flag was not set at 762, at 770, decoder 312 decodes the blockusing the string of bits that defines the block tree pattern. Decoder312 may use the function tradition_decode_root_block( ) to perform thedecoding process that does not reuse the block tree pattern.

Some embodiments can also apply patches to block tree patterns. Thepatches may modify bit values in the bit string that describes the blocktree pattern. In this case, the changes may be sent to decoder 312instead of having to send the whole encoded bit string to describe theblock tree pattern. The modification is different from the rotation orflipping of a block tree pattern. The rotation or flipping did notchange a value of the bit string describing the block tree pattern;rather, the rotation or flipping rearranged the bits to represent thealtered block tree pattern. Applying a patch, however, will change atleast one of the values of the bit string for the block tree pattern.

FIG. 8 depicts an example of applying a patch to blocks according tosome embodiments. The patch that is signaled in the encoded bitstreammay indicate a type of operation to perform on a block, such as a splitor merge. A split may split a block into multiple smaller blocks. Amerge may merge smaller blocks into a larger block or blocks. Also, thepatch may indicate how to split or merge the prior block tree pattern.

In the example in FIG. 8 , transcoder 306 identifies a root block 802that includes a block tree pattern that can be reused, and determinesthat the block tree pattern needs to be altered to be more similar tothe block tree pattern for a current block being transcoded. The blocktree pattern for a root block 803 is the result of applying a patch toroot block 802. Specifically, within root block 803, the smaller blocksat 804 have been modified from a block 806-1 in root block 802. Theadjustment may split a block further (e.g., add some split operations)or merge blocks that were split (e.g., remove some split operations). Inthe example of adding split operations, in the block shown at 806-1 inroot block 802, no split operations were performed. However, at 804-1,the block has been split twice. At 804-1, the block is split into fourblocks. Then, at 804-2, the newly formed block is split into fourblocks.

A block 806-2 in root block 802 has been split at two levels. However, ablock at 804-3 in root block 803 has not been split. To merge theblocks, at 804-4, the split of the block is removed to merge the fourblocks into one block. Also, at 804-3, the four blocks are merged into asingle block. This block now matches the block at 806-2.

The search can be performed via parsing and comparing the split bitstrings of current root block and the target block. Transcoder 306 cantolerate a certain level of differences between the two block treepatterns. For example, transcoder 306 allows the two block patterns tobe different at certain block sizes, and/or allows a maximum number ofdifferent blocks of the two block patterns. For these bits need to bechanged, transcoder 306 can perform the patches to change the bitstring.

FIG. 9A depicts a simplified flowchart 900 of a method for transcoding aroot block when reusing altered block tree patterns according to someembodiments. The following assumes that transcoder 306 has transcodedsome root blocks and stored the block tree patterns in storage. At 902,transcoder 306 searches the storage for previous block tree patternsthat may be reused, but are not the same. When a previous block treepattern that can be reused is found, but is not the same, at 904,transcoder 306 may then determine if the previous block tree pattern canbe patched to create a block tree pattern that is the same as thecurrent block tree pattern of the current root block.

At 906, if the previous block tree pattern can be patched, transcoder306 determines information for the patch of the previous block treepattern. Then, at 908, in addition to inserting a flag in the encodedbitstream indicating that the previous block tree pattern from anotherblock is being used for the current root block and the location of theroot block, transcoder 306 may insert information on how to patch theprevious block tree pattern. For example, transcoder 306 may insertinformation on whether to split or merge blocks of the previous blocktree pattern. At 910, if a patch to the previous block tree patterncannot be used, transcoder 306 inserts the full description for thecurrent block tree pattern into the encoded bitstream.

FIG. 9B depicts a simplified flowchart 930 of a method for decoding ablock when applying a patch to a previous block tree pattern accordingto some embodiments. At 932, decoder 312 selects a current root block todecode from the encoded bitstream. At 934, decoder 312 determines if aflag is set that indicates a previous block tree pattern should bereused. If the flag is set to indicate that the previous block treepattern should be reused, then at 936, decoder 312 determines thelocation of the previous block tree pattern for a previous root block.At 938, decoder 312 determines whether a patch of the previous blocktree pattern is required. If so, at 940, decoder 312 retrieves andapplies the patch to the block tree pattern for the previous root block.If a patch is not applied or after the patch is applied, at 942, decoder312 then decodes the current root block by reusing the altered blocktree pattern. If, on the other hand, the flag was not set at 934, at944, decoder 312 decodes the current root block using the string of bitsin the encoded bitstream that defines the block tree pattern.

FIG. 9C depicts an example of software code to process patches accordingto some embodiments. At 962, decoder 312 determines the value of theflag reuse_previous_tree_flag. At 964, if the flag is set to indicatethat the block tree pattern should be reused, then at 966, decoder 312determines the location of the previous block tree. For example, thelocation is stored in the variable location_of_previous_tree. Then, at968, decoder 312 determines a number of patches that are being applied.For example, transcoder 306 determines how many patches are to beapplied to the previous block tree pattern.

At 970, for each of the patches, decoder 312 performs the followingprocess. At 972, decoder 312 determines a patch starting index thatindicates where to apply the patch in the block tree pattern. At 974,decoder 312 determines the patch type, such as a split or merge. At 976,if the patch is a split, then decoder 312 determines the value for thesplit flags patch_split_flags that indicate how to split the blocks. Forexample, the split flags may indicate how many blocks to split the blockinto, and the splitting pattern inside the block. At 978, if the patchis a merge, decoder 312 determines a merge depth that describes how tomerge the blocks. For example, four blocks with size of N×N may bemerged into one larger block with size of 2N×2N, which can be specifiedby setting the merge depth equal to 0. Merge depth (plus 1) defines thenumbers of levels of the merge, so that merge depth equal to 0 specifiesa merge that is one level up (e.g., merging four blocks into one largerblock).

FIG. 10 depicts examples of a split patch and a merge patch according tosome embodiments. For a split patch, at 1002, the patch starting indexis shown as index #0. The blocks may be numbered in sequence startingfrom block 0, and in this case, the index proceeds to block #21. Thenumber of blocks depends on the block tree pattern.

At 1004, a split type patch is applied to the block at 1002. The bitstring pattern of “(1)0001000” indicates that block 0 should be splitinto four blocks and then the bottom right smaller block is split intofour more blocks. The bits correspond to the block identifiers in thequad-tree splitting and may indicate when to perform a split for theblocks. The bit string of (1)00010000 may indicate:

-   (1) : split the block 0 into four sub-blocks-   0: no further split to the 1st sub-block-   0: no further split to the 2nd sub-block-   0: no further split to the 3rd sub-block-   1: split the 4th sub-block (bottom one) into four sub-sub-blocks-   0: no further split to the 1st sub-sub-block-   0: no further split to the 2nd sub-sub-block-   0: no further split to the 3rd sub-sub-block-   0: no further split to the 4th sub-sub-block-   All leaf nodes have been reached.

Since decoder 312 has received the patch type and knows that this is asplit patch, the first split bit “(1)” can be derived and there may beno need to signal this bit. The value of first split bit “(1)” in thestring indicates splitting the larger block, which can be omittedbecause it can be implicitly derived from the split type patch. The bitsthat are transmitted may be less than the number of bits for signalingthe whole block tree pattern because only the patches to parts of thestructure are transmitted while a complicated block tree pattern mayinclude a larger number of bits.

For a merge patch, at 1006, the patch starting index is 15, which isblock 15. The patch type is a merge and the depth is equal to “1” toobtain the block shown at 1008. The depth indicates how many levels ofblocks to merge. For example, a depth of 1 indicates that blocks 15-21should be merged into one block and a depth of 0 indicates that blocks15-18 should be merged into one block. Since the depth is 1 in thisexample, decoder 312 merges blocks 15-21 into one block. The number ofbits to signal the merge is reduced because the merge depth is signaled,which may be one bit compared to the multiple bits needed to signal thewhole block tree pattern.

Conclusion

Accordingly, some embodiments reuse block tree patterns to improve thecoding efficiency. The number of bits sent in an encoded bitstream maybe reduced, which increases the compression of a video.

System

FIG. 11 depicts an example of a transcoding system according to someembodiments. A video codec framework includes a set of fundamentalcomponents: block partitioning, inter and intra prediction, transformand quantization, and entropy coding.

Transcoder 306 receives a frame of a video, which is firstly split intonon-overlapping coding blocks for further processing. To cope withdifferent video content characteristics, complex regions will be coveredby partitions with smaller sizes, while simple regions will be coveredby larger partitions. Multiple block patterns and shapes are may be bothused together, for example quad-tree pattern, triple-tree pattern andbinary-tree pattern can be all used together, while square blocks andrectangular blocks can also be used together.

Prediction is used to remove the redundancy of a video signal. Bysubtracting the predicted pixel values from the pixels being processed,the amplitude of a residual signal can be significantly reduced, thusthe resulting bitstream size can be reduced. An intra prediction block1110, which is using reference pixels in the current frame, aims toreduce the spatial redundancy within the frame. An inter predictionblock 1112, which is using reference pixels from neighboring frames,attempts to remove the temporal redundancy between frames. a motionestimation and compensation block 1116 may be a sub-module of interprediction at the transcoder side, which captures the motion trace ofobjects among adjacent frames and generates reference pixels for interprediction.

A transform and quantization block 1104 uses the residual pixels afterintra or inter prediction. Transform and quantization block 1104performs a transform operation that represents the residual signal in afrequency domain. Considering the human visual system is more sensitiveon low frequency components of video signal than the high frequencycomponents, quantization is designed to further compress the residualsignal by reducing the precision on high frequency signals.

To avoid the out-of-sync issue between transcoder 306 and decoder 312,transcoder 306 contains decoding modules to make sure both transcoder306 and decoder 312 are using identical mathematical processes. Thus, aninverse transform and inverse quantization block 1108 is similar to thesame block on the decoder side. Inverse transform and inversequantization block 1108 reconstructs pixels using the intra and interprediction.

An in-loop filter 1114 removes any visual artifacts that are introducedby the above-mentioned processes. Various filtering methods are appliedon the reconstructed frame in a cascaded way to reduce differentartifacts, including but not limited to the blocking artifacts, mosquitoartifacts, color banding effects, etc.

An entropy encoding block 1106 may further compress the bitstream usinga model-based method. Transcoder 306 transmits the resulting encodedbitstream to decoder 312 over a network or other types of medium.

FIG. 12 depicts an example of a decoding system according to someembodiments. Decoder 312 receives the encoded bitstream and inputs itinto an entropy decoding block 1202 to recover the information neededfor decoding process. As above-mentioned, a decoded frame can be decodedby using an inverse transform and inverse quantization block 1204, anintra prediction block 1206 or inter prediction block 1208, motioncompensation block 1210, and in-loop filtering block 1212 in the sameway to build a decoded frame.

Some embodiments may be implemented in a non-transitorycomputer-readable storage medium for use by or in connection with theinstruction execution system, apparatus, system, or machine. Thecomputer-readable storage medium contains instructions for controlling acomputer system to perform a method described by some embodiments. Thecomputer system may include one or more computing devices. Theinstructions, when executed by one or more computer processors, may beconfigured to perform that which is described in some embodiments.

As used in the description herein and throughout the claims that follow,“a”, “an”, and “the” includes plural references unless the contextclearly dictates otherwise. Also, as used in the description herein andthroughout the claims that follow, the meaning of “in” includes “in” and“on” unless the context clearly dictates otherwise.

The above description illustrates various embodiments along withexamples of how aspects of some embodiments may be implemented. Theabove examples and embodiments should not be deemed to be the onlyembodiments, and are presented to illustrate the flexibility andadvantages of some embodiments as defined by the following claims. Basedon the above disclosure and the following claims, other arrangements,embodiments, implementations and equivalents may be employed withoutdeparting from the scope hereof as defined by the claims.

What is claimed is:
 1. A method comprising: transcoding, by a computingdevice, a first block from a spatial region, the first block associatedwith a first block tree pattern defining a structure of splitting ablock into smaller blocks; including, by the computing device, a bitstring of bits for the first block tree pattern in an encoded bitstream;determining, by the computing device, a location of the first block inthe spatial region when the first block tree pattern of the first blockcan be reused for a second block tree pattern of a second block, whereinthe spatial region includes a plurality of blocks and the location isbased on the first block being one of the plurality of blocks in thespatial region; and including, by the computing device, information forthe second block in the encoded bitstream that indicates the location ofthe first block in the spatial region without including a bit string ofbits for the second block tree pattern, wherein the location allows thebit string of bits for the first block tree pattern to be retrieved foruse to decode the second block from the encoded bitstream.
 2. The methodof claim 1, wherein: the spatial region comprises a frame of a video,and the first block and the second block are in the frame.
 3. The methodof claim 1, wherein: the spatial region comprises a first frame, thefirst block is located in the first frame, and the second block islocated in a second frame.
 4. The method of claim 1, wherein: thespatial region comprises a first layer in a multi-layer video, and thefirst block is located in the first layer, and the second block islocated in a second layer in the multi-layer video.
 5. The method ofclaim 4, wherein: the first layer is part of a sequence of pictureshaving a first common characteristic, and the second layer is part of asequence of pictures having a second common characteristic.
 6. Themethod of claim 4, wherein: the first layer is part of a first view ofmulti-view data, and the second layer is part of a second view of themulti-view data.
 7. The method of claim 1, wherein: the spatial regioncomprises a first view in a multi-view video, the first block is locatedin the first view, and the second block is located in a second view inthe multi-view video.
 8. The method of claim 1, wherein: the pluralityof blocks comprises a plurality of root blocks, wherein a root block issplit into a set of smaller blocks.
 9. The method of claim 1, wherein:the first block is a first root block, and the second block is a secondroot block.
 10. The method of claim 1, wherein: the second block treepattern defines a same structure of the first block tree pattern. 11.The method of claim 1, further comprising: determining that the firstblock tree pattern can be reused for the second block tree pattern. 12.The method of claim 1, further comprising: searching storage for asimilar block tree pattern to the second block tree pattern to determinewhen the first block tree pattern of the first block can be reused forthe second block tree pattern of the second block.
 13. An apparatuscomprising: one or more computer processors; and a non-transitorycomputer-readable storage medium comprising instructions, that whenexecuted, control the one or more computer processors to be configuredfor: transcoding a first block from a spatial region, the first blockassociated with a first block tree pattern defining a structure ofsplitting a block into smaller blocks; including a bit string of bitsfor the first block tree pattern in an encoded bitstream; determining alocation of the first block in the spatial region when the first blocktree pattern of the first block can be reused for a second block treepattern of a second block, wherein the spatial region includes aplurality of blocks and the location is based on the first block beingone of the plurality of blocks in the spatial region; and includinginformation for the second block in the encoded bitstream that indicatesthe location of the first block in the spatial region without includinga bit string of bits for the second block tree pattern, wherein thelocation allows the bit string of bits for the first block tree patternto be retrieved for use to decode the second block from the encodedbitstream.
 14. A method comprising: receiving, by a computing device, anencoded bitstream; decoding, by the computing device, a first block in aspatial region using a first block tree pattern that defines a structureof splitting the first block into smaller blocks; selecting, by thecomputing device, a second block for decoding; determining, by thecomputing device, information for the second block in the encodedbitstream that indicates a location of the first block inside thespatial region, wherein the spatial region includes a plurality ofblocks and the location is based on the first block being one of theplurality of blocks in the spatial region, and wherein the encodedbitstream does not include a bit string of bits for a second block treepattern of the second block; retrieving, by the computing device, thebit string of bits for the first block tree pattern using the location,wherein the first block tree pattern is to be used to decode the secondblock from the encoded bitstream; and decoding, by the computing device,the second block using the first block tree pattern.
 15. The method ofclaim 14, wherein: the spatial region comprises a frame of a video, andthe first block and the second block are in the frame.
 16. The method ofclaim 14, wherein: the spatial region comprises a first frame, the firstblock is located in the first frame, and the second block is located ina second frame.
 17. The method of claim 14, wherein: the spatial regioncomprises a first layer in a multi-layer video, and the first block islocated in the first layer, and the second block is located in a secondlayer in the multi-layer video.
 18. The method of claim 17, wherein: thefirst layer is part of a sequence of pictures having a first commoncharacteristic, and the second layer is part of a sequence of pictureshaving a second common characteristic.
 19. The method of claim 17,wherein: the first layer is part of a first view of multi-view data, andthe second layer is part of a second view of the multi-view data. 20.The method of claim 14, wherein: the spatial region comprises a firstview in a multi-view video, the first block is located in the firstview, and the second block is located in a second view in the multi-viewvideo.